The Rydberg states of alkali/rare-gas diatomic molecules show complex potential energy curves due to two effects: (1) avoided crossings between two close atomic cofigurations, and (2) undulations originating from the atomic orbital structures of the alkali Rydberg states. This work reports the potential energy curves for ten (2)Sigma (+) states correlated to the atomic states from Na(3s) to Na(6s) obtained from accurate ab initio calculations. We give the spectroscopic constants and present a complete analysis for these potential curves.